New silane-containing universal adhesives: Reactivity, wettability and bonding capacity with lithium-disilicate...

To assess the silane reactivity, wettability and bond strength with a Lithium (Li)-disilicate ceramic in a series of new silane-containing universal adhesives.

Five adhesives (BeautiBond Xtreme-BXB, Clearfil Universal Bond Quick 2-CBQ, Scotchbond Universal Plus-SUP, Tokuyama Universal Bond II-TUB) and a universal silane primer control (Clearfil Ceramic Primer Plus-CCP) were tested. Residual silanol (RS%) and siloxane formation (SF) rates of thin silane films were monitored by FTIR spectroscopy (0, 10, 30, 60 min storage-60% relative humidity). Wettability was assessed on hydrofluoric acid-etched Li-disilicate surfaces after 60 min storage by water contact angle measurements (WCA, before/after ethanol rinsing). Finally, the shear bond strength (SBS) of a resin composite to etched and silane-treated ceramic surfaces was evaluated following 1-week water storage (37 °C), before and after accelerated aging (24-h boiling water test).

SUP and TUB demonstrated lower RS% and full silanol consumption (30 min-SUP, 60 min-TUB) in comparison with other materials (>60% at 60 min). The highest SF was found in TUB, followed by SUP and all other materials (lower values). All treatments resulted in hydrophilic surfaces, with greater WCA in TUB, CCP (before), in TUB, CBQ, CCP (after ethanol rinsing), and in all paired comparisons (before-after, in favor of the latter) except for SUP. The ranking of the SBS values was TUB, SUP > BXB, CBQ, CCP (before and after aging), with a significant reduction after aging (-67 up to -54 %).

The silanes contained in the new universal adhesives demonstrated silanol condensation, with great differences in the reaction rates and wettability dependent on composition and setting mechanisms. However, all products failed to provide water-repellent interfaces, leading to hydrolytic instability after accelerated aging.